/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.feilong.lib.lang3.time;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.io.UncheckedIOException;
import java.text.DateFormat;
import java.text.DateFormatSymbols;
import java.text.FieldPosition;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.Locale;
import java.util.TimeZone;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * <p>
 * FastDatePrinter is a fast and thread-safe version of
 * {@link java.text.SimpleDateFormat}.
 * </p>
 *
 * <p>
 * To obtain a FastDatePrinter, use {@link FastDateFormat#getInstance(String, TimeZone, Locale)}
 * or another variation of the factory methods of {@link FastDateFormat}.
 * </p>
 *
 * <p>
 * Since FastDatePrinter is thread safe, you can use a static member instance:
 * </p>
 * <code>
 *     private static final DatePrinter DATE_PRINTER = FastDateFormat.getInstance("yyyy-MM-dd");
 * </code>
 *
 * <p>
 * This class can be used as a direct replacement to
 * {@code SimpleDateFormat} in most formatting situations.
 * This class is especially useful in multi-threaded server environments.
 * {@code SimpleDateFormat} is not thread-safe in any JDK version,
 * nor will it be as Sun have closed the bug/RFE.
 * </p>
 *
 * <p>
 * Only formatting is supported by this class, but all patterns are compatible with
 * SimpleDateFormat (except time zones and some year patterns - see below).
 * </p>
 *
 * <p>
 * Java 1.4 introduced a new pattern letter, {@code 'Z'}, to represent
 * time zones in RFC822 format (eg. {@code +0800} or {@code -1100}).
 * This pattern letter can be used here (on all JDK versions).
 * </p>
 *
 * <p>
 * In addition, the pattern {@code 'ZZ'} has been made to represent
 * ISO 8601 extended format time zones (eg. {@code +08:00} or {@code -11:00}).
 * This introduces a minor incompatibility with Java 1.4, but at a gain of
 * useful functionality.
 * </p>
 *
 * <p>
 * Starting with JDK7, ISO 8601 support was added using the pattern {@code 'X'}.
 * To maintain compatibility, {@code 'ZZ'} will continue to be supported, but using
 * one of the {@code 'X'} formats is recommended.
 *
 * <p>
 * Javadoc cites for the year pattern: <i>For formatting, if the number of
 * pattern letters is 2, the year is truncated to 2 digits; otherwise it is
 * interpreted as a number.</i> Starting with Java 1.7 a pattern of 'Y' or
 * 'YYY' will be formatted as '2003', while it was '03' in former Java
 * versions. FastDatePrinter implements the behavior of Java 7.
 * </p>
 *
 * @since 3.2
 * @see FastDateParser
 */
public class FastDatePrinter implements DatePrinter,Serializable{
    // A lot of the speed in this class comes from caching, but some comes
    // from the special int to StringBuffer conversion.
    //
    // The following produces a padded 2 digit number:
    //   buffer.append((char)(value / 10 + '0'));
    //   buffer.append((char)(value % 10 + '0'));
    //
    // Note that the fastest append to StringBuffer is a single char (used here).
    // Note that Integer.toString() is not called, the conversion is simply
    // taking the value and adding (mathematically) the ASCII value for '0'.
    // So, don't change this code! It works and is very fast.

    /**
     * Required for serialization support.
     *
     * @see java.io.Serializable
     */
    private static final long serialVersionUID = 1L;

    /**
     * FULL locale dependent date or time style.
     */
    public static final int   FULL             = DateFormat.FULL;

    /**
     * LONG locale dependent date or time style.
     */
    public static final int   LONG             = DateFormat.LONG;

    /**
     * MEDIUM locale dependent date or time style.
     */
    public static final int   MEDIUM           = DateFormat.MEDIUM;

    /**
     * SHORT locale dependent date or time style.
     */
    public static final int   SHORT            = DateFormat.SHORT;

    /**
     * The pattern.
     */
    private final String      mPattern;

    /**
     * The time zone.
     */
    private final TimeZone    mTimeZone;

    /**
     * The locale.
     */
    private final Locale      mLocale;

    /**
     * The parsed rules.
     */
    private transient Rule[]  mRules;

    /**
     * The estimated maximum length.
     */
    private transient int     mMaxLengthEstimate;

    // Constructor
    //-----------------------------------------------------------------------
    /**
     * <p>
     * Constructs a new FastDatePrinter.
     * </p>
     * Use {@link FastDateFormat#getInstance(String, TimeZone, Locale)} or another variation of the
     * factory methods of {@link FastDateFormat} to get a cached FastDatePrinter instance.
     *
     * @param pattern
     *            {@link java.text.SimpleDateFormat} compatible pattern
     * @param timeZone
     *            non-null time zone to use
     * @param locale
     *            non-null locale to use
     * @throws NullPointerException
     *             if pattern, timeZone, or locale is null.
     */
    protected FastDatePrinter(final String pattern, final TimeZone timeZone, final Locale locale){
        mPattern = pattern;
        mTimeZone = timeZone;
        mLocale = locale;

        init();
    }

    /**
     * <p>
     * Initializes the instance for first use.
     * </p>
     */
    private void init(){
        final List<Rule> rulesList = parsePattern();
        mRules = rulesList.toArray(new Rule[0]);

        int len = 0;
        for (int i = mRules.length; --i >= 0;){
            len += mRules[i].estimateLength();
        }

        mMaxLengthEstimate = len;
    }

    // Parse the pattern
    //-----------------------------------------------------------------------
    /**
     * <p>
     * Returns a list of Rules given a pattern.
     * </p>
     *
     * @return a {@code List} of Rule objects
     * @throws IllegalArgumentException
     *             if pattern is invalid
     */
    protected List<Rule> parsePattern(){
        final DateFormatSymbols symbols = new DateFormatSymbols(mLocale);
        final List<Rule> rules = new ArrayList<>();

        final String[] ERAs = symbols.getEras();
        final String[] months = symbols.getMonths();
        final String[] shortMonths = symbols.getShortMonths();
        final String[] weekdays = symbols.getWeekdays();
        final String[] shortWeekdays = symbols.getShortWeekdays();
        final String[] AmPmStrings = symbols.getAmPmStrings();

        final int length = mPattern.length();
        final int[] indexRef = new int[1];

        for (int i = 0; i < length; i++){
            indexRef[0] = i;
            final String token = parseToken(mPattern, indexRef);
            i = indexRef[0];

            final int tokenLen = token.length();
            if (tokenLen == 0){
                break;
            }

            Rule rule;
            final char c = token.charAt(0);

            switch (c) {
                case 'G': // era designator (text)
                    rule = new TextField(Calendar.ERA, ERAs);
                    break;
                case 'y': // year (number)
                case 'Y': // week year
                    if (tokenLen == 2){
                        rule = TwoDigitYearField.INSTANCE;
                    }else{
                        rule = selectNumberRule(Calendar.YEAR, tokenLen < 4 ? 4 : tokenLen);
                    }
                    if (c == 'Y'){
                        rule = new WeekYear((NumberRule) rule);
                    }
                    break;
                case 'M': // month in year (text and number)
                    if (tokenLen >= 4){
                        rule = new TextField(Calendar.MONTH, months);
                    }else if (tokenLen == 3){
                        rule = new TextField(Calendar.MONTH, shortMonths);
                    }else if (tokenLen == 2){
                        rule = TwoDigitMonthField.INSTANCE;
                    }else{
                        rule = UnpaddedMonthField.INSTANCE;
                    }
                    break;
                case 'd': // day in month (number)
                    rule = selectNumberRule(Calendar.DAY_OF_MONTH, tokenLen);
                    break;
                case 'h': // hour in am/pm (number, 1..12)
                    rule = new TwelveHourField(selectNumberRule(Calendar.HOUR, tokenLen));
                    break;
                case 'H': // hour in day (number, 0..23)
                    rule = selectNumberRule(Calendar.HOUR_OF_DAY, tokenLen);
                    break;
                case 'm': // minute in hour (number)
                    rule = selectNumberRule(Calendar.MINUTE, tokenLen);
                    break;
                case 's': // second in minute (number)
                    rule = selectNumberRule(Calendar.SECOND, tokenLen);
                    break;
                case 'S': // millisecond (number)
                    rule = selectNumberRule(Calendar.MILLISECOND, tokenLen);
                    break;
                case 'E': // day in week (text)
                    rule = new TextField(Calendar.DAY_OF_WEEK, tokenLen < 4 ? shortWeekdays : weekdays);
                    break;
                case 'u': // day in week (number)
                    rule = new DayInWeekField(selectNumberRule(Calendar.DAY_OF_WEEK, tokenLen));
                    break;
                case 'D': // day in year (number)
                    rule = selectNumberRule(Calendar.DAY_OF_YEAR, tokenLen);
                    break;
                case 'F': // day of week in month (number)
                    rule = selectNumberRule(Calendar.DAY_OF_WEEK_IN_MONTH, tokenLen);
                    break;
                case 'w': // week in year (number)
                    rule = selectNumberRule(Calendar.WEEK_OF_YEAR, tokenLen);
                    break;
                case 'W': // week in month (number)
                    rule = selectNumberRule(Calendar.WEEK_OF_MONTH, tokenLen);
                    break;
                case 'a': // am/pm marker (text)
                    rule = new TextField(Calendar.AM_PM, AmPmStrings);
                    break;
                case 'k': // hour in day (1..24)
                    rule = new TwentyFourHourField(selectNumberRule(Calendar.HOUR_OF_DAY, tokenLen));
                    break;
                case 'K': // hour in am/pm (0..11)
                    rule = selectNumberRule(Calendar.HOUR, tokenLen);
                    break;
                case 'X': // ISO 8601
                    rule = Iso8601_Rule.getRule(tokenLen);
                    break;
                case 'z': // time zone (text)
                    if (tokenLen >= 4){
                        rule = new TimeZoneNameRule(mTimeZone, mLocale, TimeZone.LONG);
                    }else{
                        rule = new TimeZoneNameRule(mTimeZone, mLocale, TimeZone.SHORT);
                    }
                    break;
                case 'Z': // time zone (value)
                    if (tokenLen == 1){
                        rule = TimeZoneNumberRule.INSTANCE_NO_COLON;
                    }else if (tokenLen == 2){
                        rule = Iso8601_Rule.ISO8601_HOURS_COLON_MINUTES;
                    }else{
                        rule = TimeZoneNumberRule.INSTANCE_COLON;
                    }
                    break;
                case '\'': // literal text
                    final String sub = token.substring(1);
                    if (sub.length() == 1){
                        rule = new CharacterLiteral(sub.charAt(0));
                    }else{
                        rule = new StringLiteral(sub);
                    }
                    break;
                default:
                    throw new IllegalArgumentException("Illegal pattern component: " + token);
            }

            rules.add(rule);
        }

        return rules;
    }

    /**
     * <p>
     * Performs the parsing of tokens.
     * </p>
     *
     * @param pattern
     *            the pattern
     * @param indexRef
     *            index references
     * @return parsed token
     */
    protected String parseToken(final String pattern,final int[] indexRef){
        final StringBuilder buf = new StringBuilder();

        int i = indexRef[0];
        final int length = pattern.length();

        char c = pattern.charAt(i);
        if (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z'){
            // Scan a run of the same character, which indicates a time
            // pattern.
            buf.append(c);

            while (i + 1 < length){
                final char peek = pattern.charAt(i + 1);
                if (peek == c){
                    buf.append(c);
                    i++;
                }else{
                    break;
                }
            }
        }else{
            // This will identify token as text.
            buf.append('\'');

            boolean inLiteral = false;

            for (; i < length; i++){
                c = pattern.charAt(i);

                if (c == '\''){
                    if (i + 1 < length && pattern.charAt(i + 1) == '\''){
                        // '' is treated as escaped '
                        i++;
                        buf.append(c);
                    }else{
                        inLiteral = !inLiteral;
                    }
                }else if (!inLiteral && (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z')){
                    i--;
                    break;
                }else{
                    buf.append(c);
                }
            }
        }

        indexRef[0] = i;
        return buf.toString();
    }

    /**
     * <p>
     * Gets an appropriate rule for the padding required.
     * </p>
     *
     * @param field
     *            the field to get a rule for
     * @param padding
     *            the padding required
     * @return a new rule with the correct padding
     */
    protected NumberRule selectNumberRule(final int field,final int padding){
        switch (padding) {
            case 1:
                return new UnpaddedNumberField(field);
            case 2:
                return new TwoDigitNumberField(field);
            default:
                return new PaddedNumberField(field, padding);
        }
    }

    // Format methods
    //-----------------------------------------------------------------------
    /**
     * <p>
     * Formats a {@code Date}, {@code Calendar} or
     * {@code Long} (milliseconds) object.
     * </p>
     * 
     * @deprecated Use {{@link #format(Date)}, {{@link #format(Calendar)}, {{@link #format(long)}, or {{@link #format(Object)}
     * @param obj
     *            the object to format
     * @param toAppendTo
     *            the buffer to append to
     * @param pos
     *            the position - ignored
     * @return the buffer passed in
     */
    @Deprecated
    @Override
    public StringBuffer format(final Object obj,final StringBuffer toAppendTo,final FieldPosition pos){
        if (obj instanceof Date){
            return format((Date) obj, toAppendTo);
        }else if (obj instanceof Calendar){
            return format((Calendar) obj, toAppendTo);
        }else if (obj instanceof Long){
            return format(((Long) obj).longValue(), toAppendTo);
        }else{
            throw new IllegalArgumentException("Unknown class: " + (obj == null ? "<null>" : obj.getClass().getName()));
        }
    }

    /**
     * <p>
     * Formats a {@code Date}, {@code Calendar} or
     * {@code Long} (milliseconds) object.
     * </p>
     * 
     * @since 3.5
     * @param obj
     *            the object to format
     * @return The formatted value.
     */
    String format(final Object obj){
        if (obj instanceof Date){
            return format((Date) obj);
        }else if (obj instanceof Calendar){
            return format((Calendar) obj);
        }else if (obj instanceof Long){
            return format(((Long) obj).longValue());
        }else{
            throw new IllegalArgumentException("Unknown class: " + (obj == null ? "<null>" : obj.getClass().getName()));
        }
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(long)
     */
    @Override
    public String format(final long millis){
        final Calendar c = newCalendar();
        c.setTimeInMillis(millis);
        return applyRulesToString(c);
    }

    /**
     * Creates a String representation of the given Calendar by applying the rules of this printer to it.
     * 
     * @param c
     *            the Calender to apply the rules to.
     * @return a String representation of the given Calendar.
     */
    private String applyRulesToString(final Calendar c){
        return applyRules(c, new StringBuilder(mMaxLengthEstimate)).toString();
    }

    /**
     * Creation method for new calender instances.
     * 
     * @return a new Calendar instance.
     */
    private Calendar newCalendar(){
        return Calendar.getInstance(mTimeZone, mLocale);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date)
     */
    @Override
    public String format(final Date date){
        final Calendar c = newCalendar();
        c.setTime(date);
        return applyRulesToString(c);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar)
     */
    @Override
    public String format(final Calendar calendar){
        return format(calendar, new StringBuilder(mMaxLengthEstimate)).toString();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(long, java.lang.StringBuffer)
     */
    @Override
    public StringBuffer format(final long millis,final StringBuffer buf){
        final Calendar c = newCalendar();
        c.setTimeInMillis(millis);
        return (StringBuffer) applyRules(c, (Appendable) buf);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date, java.lang.StringBuffer)
     */
    @Override
    public StringBuffer format(final Date date,final StringBuffer buf){
        final Calendar c = newCalendar();
        c.setTime(date);
        return (StringBuffer) applyRules(c, (Appendable) buf);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar, java.lang.StringBuffer)
     */
    @Override
    public StringBuffer format(final Calendar calendar,final StringBuffer buf){
        // do not pass in calendar directly, this will cause TimeZone of FastDatePrinter to be ignored
        return format(calendar.getTime(), buf);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(long, java.lang.Appendable)
     */
    @Override
    public <B extends Appendable> B format(final long millis,final B buf){
        final Calendar c = newCalendar();
        c.setTimeInMillis(millis);
        return applyRules(c, buf);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Date, java.lang.Appendable)
     */
    @Override
    public <B extends Appendable> B format(final Date date,final B buf){
        final Calendar c = newCalendar();
        c.setTime(date);
        return applyRules(c, buf);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#format(java.util.Calendar, java.lang.Appendable)
     */
    @Override
    public <B extends Appendable> B format(Calendar calendar,final B buf){
        // do not pass in calendar directly, this will cause TimeZone of FastDatePrinter to be ignored
        if (!calendar.getTimeZone().equals(mTimeZone)){
            calendar = (Calendar) calendar.clone();
            calendar.setTimeZone(mTimeZone);
        }
        return applyRules(calendar, buf);
    }

    /**
     * Performs the formatting by applying the rules to the
     * specified calendar.
     *
     * @param calendar
     *            the calendar to format
     * @param buf
     *            the buffer to format into
     * @return the specified string buffer
     *
     * @deprecated use {@link #format(Calendar)} or {@link #format(Calendar, Appendable)}
     */
    @Deprecated
    protected StringBuffer applyRules(final Calendar calendar,final StringBuffer buf){
        return (StringBuffer) applyRules(calendar, (Appendable) buf);
    }

    /**
     * <p>
     * Performs the formatting by applying the rules to the
     * specified calendar.
     * </p>
     *
     * @param calendar
     *            the calendar to format
     * @param buf
     *            the buffer to format into
     * @param <B>
     *            the Appendable class type, usually StringBuilder or StringBuffer.
     * @return the specified string buffer
     */
    private <B extends Appendable> B applyRules(final Calendar calendar,final B buf){
        try{
            for (final Rule rule : mRules){
                rule.appendTo(buf, calendar);
            }
        }catch (final IOException ioe){
            throw new UncheckedIOException(ioe);
        }
        return buf;
    }

    // Accessors
    //-----------------------------------------------------------------------
    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#getPattern()
     */
    @Override
    public String getPattern(){
        return mPattern;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#getTimeZone()
     */
    @Override
    public TimeZone getTimeZone(){
        return mTimeZone;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.commons.lang3.time.DatePrinter#getLocale()
     */
    @Override
    public Locale getLocale(){
        return mLocale;
    }

    /**
     * <p>
     * Gets an estimate for the maximum string length that the
     * formatter will produce.
     * </p>
     *
     * <p>
     * The actual formatted length will almost always be less than or
     * equal to this amount.
     * </p>
     *
     * @return the maximum formatted length
     */
    public int getMaxLengthEstimate(){
        return mMaxLengthEstimate;
    }

    // Basics
    //-----------------------------------------------------------------------
    /**
     * <p>
     * Compares two objects for equality.
     * </p>
     *
     * @param obj
     *            the object to compare to
     * @return {@code true} if equal
     */
    @Override
    public boolean equals(final Object obj){
        if (!(obj instanceof FastDatePrinter)){
            return false;
        }
        final FastDatePrinter other = (FastDatePrinter) obj;
        return mPattern.equals(other.mPattern) && mTimeZone.equals(other.mTimeZone) && mLocale.equals(other.mLocale);
    }

    /**
     * <p>
     * Returns a hash code compatible with equals.
     * </p>
     *
     * @return a hash code compatible with equals
     */
    @Override
    public int hashCode(){
        return mPattern.hashCode() + 13 * (mTimeZone.hashCode() + 13 * mLocale.hashCode());
    }

    /**
     * <p>
     * Gets a debugging string version of this formatter.
     * </p>
     *
     * @return a debugging string
     */
    @Override
    public String toString(){
        return "FastDatePrinter[" + mPattern + "," + mLocale + "," + mTimeZone.getID() + "]";
    }

    // Serializing
    //-----------------------------------------------------------------------
    /**
     * Create the object after serialization. This implementation reinitializes the
     * transient properties.
     *
     * @param in
     *            ObjectInputStream from which the object is being deserialized.
     * @throws IOException
     *             if there is an IO issue.
     * @throws ClassNotFoundException
     *             if a class cannot be found.
     */
    private void readObject(final ObjectInputStream in) throws IOException,ClassNotFoundException{
        in.defaultReadObject();
        init();
    }

    /**
     * Appends two digits to the given buffer.
     *
     * @param buffer
     *            the buffer to append to.
     * @param value
     *            the value to append digits from.
     */
    private static void appendDigits(final Appendable buffer,final int value) throws IOException{
        buffer.append((char) (value / 10 + '0'));
        buffer.append((char) (value % 10 + '0'));
    }

    private static final int MAX_DIGITS = 10; // log10(Integer.MAX_VALUE) ~= 9.3

    /**
     * Appends all digits to the given buffer.
     *
     * @param buffer
     *            the buffer to append to.
     * @param value
     *            the value to append digits from.
     */
    private static void appendFullDigits(final Appendable buffer,int value,int minFieldWidth) throws IOException{
        // specialized paths for 1 to 4 digits -> avoid the memory allocation from the temporary work array
        // see LANG-1248
        if (value < 10000){
            // less memory allocation path works for four digits or less

            int nDigits = 4;
            if (value < 1000){
                --nDigits;
                if (value < 100){
                    --nDigits;
                    if (value < 10){
                        --nDigits;
                    }
                }
            }
            // left zero pad
            for (int i = minFieldWidth - nDigits; i > 0; --i){
                buffer.append('0');
            }

            switch (nDigits) {
                case 4:
                    buffer.append((char) (value / 1000 + '0'));
                    value %= 1000;
                case 3:
                    if (value >= 100){
                        buffer.append((char) (value / 100 + '0'));
                        value %= 100;
                    }else{
                        buffer.append('0');
                    }
                case 2:
                    if (value >= 10){
                        buffer.append((char) (value / 10 + '0'));
                        value %= 10;
                    }else{
                        buffer.append('0');
                    }
                case 1:
                    buffer.append((char) (value + '0'));
            }
        }else{
            // more memory allocation path works for any digits

            // build up decimal representation in reverse
            final char[] work = new char[MAX_DIGITS];
            int digit = 0;
            while (value != 0){
                work[digit++] = (char) (value % 10 + '0');
                value = value / 10;
            }

            // pad with zeros
            while (digit < minFieldWidth){
                buffer.append('0');
                --minFieldWidth;
            }

            // reverse
            while (--digit >= 0){
                buffer.append(work[digit]);
            }
        }
    }

    // Rules
    //-----------------------------------------------------------------------
    /**
     * <p>
     * Inner class defining a rule.
     * </p>
     */
    private interface Rule{

        /**
         * Returns the estimated length of the result.
         *
         * @return the estimated length
         */
        int estimateLength();

        /**
         * Appends the value of the specified calendar to the output buffer based on the rule implementation.
         *
         * @param buf
         *            the output buffer
         * @param calendar
         *            calendar to be appended
         * @throws IOException
         *             if an I/O error occurs
         */
        void appendTo(Appendable buf,Calendar calendar) throws IOException;
    }

    /**
     * <p>
     * Inner class defining a numeric rule.
     * </p>
     */
    private interface NumberRule extends Rule{

        /**
         * Appends the specified value to the output buffer based on the rule implementation.
         *
         * @param buffer
         *            the output buffer
         * @param value
         *            the value to be appended
         * @throws IOException
         *             if an I/O error occurs
         */
        void appendTo(Appendable buffer,int value) throws IOException;
    }

    /**
     * <p>
     * Inner class to output a constant single character.
     * </p>
     */
    private static class CharacterLiteral implements Rule{

        private final char mValue;

        /**
         * Constructs a new instance of {@code CharacterLiteral}
         * to hold the specified value.
         *
         * @param value
         *            the character literal
         */
        CharacterLiteral(final char value){
            mValue = value;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 1;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            buffer.append(mValue);
        }
    }

    /**
     * <p>
     * Inner class to output a constant string.
     * </p>
     */
    private static class StringLiteral implements Rule{

        private final String mValue;

        /**
         * Constructs a new instance of {@code StringLiteral}
         * to hold the specified value.
         *
         * @param value
         *            the string literal
         */
        StringLiteral(final String value){
            mValue = value;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return mValue.length();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            buffer.append(mValue);
        }
    }

    /**
     * <p>
     * Inner class to output one of a set of values.
     * </p>
     */
    private static class TextField implements Rule{

        private final int      mField;

        private final String[] mValues;

        /**
         * Constructs an instance of {@code TextField}
         * with the specified field and values.
         *
         * @param field
         *            the field
         * @param values
         *            the field values
         */
        TextField(final int field, final String[] values){
            mField = field;
            mValues = values;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            int max = 0;
            for (int i = mValues.length; --i >= 0;){
                final int len = mValues[i].length();
                if (len > max){
                    max = len;
                }
            }
            return max;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            buffer.append(mValues[calendar.get(mField)]);
        }
    }

    /**
     * <p>
     * Inner class to output an unpadded number.
     * </p>
     */
    private static class UnpaddedNumberField implements NumberRule{

        private final int mField;

        /**
         * Constructs an instance of {@code UnpadedNumberField} with the specified field.
         *
         * @param field
         *            the field
         */
        UnpaddedNumberField(final int field){
            mField = field;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 4;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            if (value < 10){
                buffer.append((char) (value + '0'));
            }else if (value < 100){
                appendDigits(buffer, value);
            }else{
                appendFullDigits(buffer, value, 1);
            }
        }
    }

    /**
     * <p>
     * Inner class to output an unpadded month.
     * </p>
     */
    private static class UnpaddedMonthField implements NumberRule{

        static final UnpaddedMonthField INSTANCE = new UnpaddedMonthField();

        /**
         * Constructs an instance of {@code UnpaddedMonthField}.
         *
         */
        UnpaddedMonthField(){
            super();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            if (value < 10){
                buffer.append((char) (value + '0'));
            }else{
                appendDigits(buffer, value);
            }
        }
    }

    /**
     * <p>
     * Inner class to output a padded number.
     * </p>
     */
    private static class PaddedNumberField implements NumberRule{

        private final int mField;

        private final int mSize;

        /**
         * Constructs an instance of {@code PaddedNumberField}.
         *
         * @param field
         *            the field
         * @param size
         *            size of the output field
         */
        PaddedNumberField(final int field, final int size){
            if (size < 3){
                // Should use UnpaddedNumberField or TwoDigitNumberField.
                throw new IllegalArgumentException();
            }
            mField = field;
            mSize = size;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return mSize;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            appendFullDigits(buffer, value, mSize);
        }
    }

    /**
     * <p>
     * Inner class to output a two digit number.
     * </p>
     */
    private static class TwoDigitNumberField implements NumberRule{

        private final int mField;

        /**
         * Constructs an instance of {@code TwoDigitNumberField} with the specified field.
         *
         * @param field
         *            the field
         */
        TwoDigitNumberField(final int field){
            mField = field;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(mField));
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            if (value < 100){
                appendDigits(buffer, value);
            }else{
                appendFullDigits(buffer, value, 2);
            }
        }
    }

    /**
     * <p>
     * Inner class to output a two digit year.
     * </p>
     */
    private static class TwoDigitYearField implements NumberRule{

        static final TwoDigitYearField INSTANCE = new TwoDigitYearField();

        /**
         * Constructs an instance of {@code TwoDigitYearField}.
         */
        TwoDigitYearField(){
            super();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(Calendar.YEAR) % 100);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            appendDigits(buffer, value);
        }
    }

    /**
     * <p>
     * Inner class to output a two digit month.
     * </p>
     */
    private static class TwoDigitMonthField implements NumberRule{

        static final TwoDigitMonthField INSTANCE = new TwoDigitMonthField();

        /**
         * Constructs an instance of {@code TwoDigitMonthField}.
         */
        TwoDigitMonthField(){
            super();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 2;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            appendTo(buffer, calendar.get(Calendar.MONTH) + 1);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public final void appendTo(final Appendable buffer,final int value) throws IOException{
            appendDigits(buffer, value);
        }
    }

    /**
     * <p>
     * Inner class to output the twelve hour field.
     * </p>
     */
    private static class TwelveHourField implements NumberRule{

        private final NumberRule mRule;

        /**
         * Constructs an instance of {@code TwelveHourField} with the specified
         * {@code NumberRule}.
         *
         * @param rule
         *            the rule
         */
        TwelveHourField(final NumberRule rule){
            mRule = rule;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return mRule.estimateLength();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            int value = calendar.get(Calendar.HOUR);
            if (value == 0){
                value = calendar.getLeastMaximum(Calendar.HOUR) + 1;
            }
            mRule.appendTo(buffer, value);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final int value) throws IOException{
            mRule.appendTo(buffer, value);
        }
    }

    /**
     * <p>
     * Inner class to output the twenty four hour field.
     * </p>
     */
    private static class TwentyFourHourField implements NumberRule{

        private final NumberRule mRule;

        /**
         * Constructs an instance of {@code TwentyFourHourField} with the specified
         * {@code NumberRule}.
         *
         * @param rule
         *            the rule
         */
        TwentyFourHourField(final NumberRule rule){
            mRule = rule;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return mRule.estimateLength();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            int value = calendar.get(Calendar.HOUR_OF_DAY);
            if (value == 0){
                value = calendar.getMaximum(Calendar.HOUR_OF_DAY) + 1;
            }
            mRule.appendTo(buffer, value);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final int value) throws IOException{
            mRule.appendTo(buffer, value);
        }
    }

    /**
     * <p>
     * Inner class to output the numeric day in week.
     * </p>
     */
    private static class DayInWeekField implements NumberRule{

        private final NumberRule mRule;

        DayInWeekField(final NumberRule rule){
            mRule = rule;
        }

        @Override
        public int estimateLength(){
            return mRule.estimateLength();
        }

        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            final int value = calendar.get(Calendar.DAY_OF_WEEK);
            mRule.appendTo(buffer, value == Calendar.SUNDAY ? 7 : value - 1);
        }

        @Override
        public void appendTo(final Appendable buffer,final int value) throws IOException{
            mRule.appendTo(buffer, value);
        }
    }

    /**
     * <p>
     * Inner class to output the numeric day in week.
     * </p>
     */
    private static class WeekYear implements NumberRule{

        private final NumberRule mRule;

        WeekYear(final NumberRule rule){
            mRule = rule;
        }

        @Override
        public int estimateLength(){
            return mRule.estimateLength();
        }

        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            mRule.appendTo(buffer, calendar.getWeekYear());
        }

        @Override
        public void appendTo(final Appendable buffer,final int value) throws IOException{
            mRule.appendTo(buffer, value);
        }
    }

    //-----------------------------------------------------------------------

    private static final ConcurrentMap<TimeZoneDisplayKey, String> cTimeZoneDisplayCache = new ConcurrentHashMap<>(7);

    /**
     * <p>
     * Gets the time zone display name, using a cache for performance.
     * </p>
     *
     * @param tz
     *            the zone to query
     * @param daylight
     *            true if daylight savings
     * @param style
     *            the style to use {@code TimeZone.LONG} or {@code TimeZone.SHORT}
     * @param locale
     *            the locale to use
     * @return the textual name of the time zone
     */
    static String getTimeZoneDisplay(final TimeZone tz,final boolean daylight,final int style,final Locale locale){
        final TimeZoneDisplayKey key = new TimeZoneDisplayKey(tz, daylight, style, locale);
        String value = cTimeZoneDisplayCache.get(key);
        if (value == null){
            // This is a very slow call, so cache the results.
            value = tz.getDisplayName(daylight, style, locale);
            final String prior = cTimeZoneDisplayCache.putIfAbsent(key, value);
            if (prior != null){
                value = prior;
            }
        }
        return value;
    }

    /**
     * <p>
     * Inner class to output a time zone name.
     * </p>
     */
    private static class TimeZoneNameRule implements Rule{

        private final Locale mLocale;

        private final int    mStyle;

        private final String mStandard;

        private final String mDaylight;

        /**
         * Constructs an instance of {@code TimeZoneNameRule} with the specified properties.
         *
         * @param timeZone
         *            the time zone
         * @param locale
         *            the locale
         * @param style
         *            the style
         */
        TimeZoneNameRule(final TimeZone timeZone, final Locale locale, final int style){
            mLocale = locale;
            mStyle = style;

            mStandard = getTimeZoneDisplay(timeZone, false, style, locale);
            mDaylight = getTimeZoneDisplay(timeZone, true, style, locale);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            // We have no access to the Calendar object that will be passed to
            // appendTo so base estimate on the TimeZone passed to the
            // constructor
            return Math.max(mStandard.length(), mDaylight.length());
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            final TimeZone zone = calendar.getTimeZone();
            if (calendar.get(Calendar.DST_OFFSET) == 0){
                buffer.append(getTimeZoneDisplay(zone, false, mStyle, mLocale));
            }else{
                buffer.append(getTimeZoneDisplay(zone, true, mStyle, mLocale));
            }
        }
    }

    /**
     * <p>
     * Inner class to output a time zone as a number {@code +/-HHMM}
     * or {@code +/-HH:MM}.
     * </p>
     */
    private static class TimeZoneNumberRule implements Rule{

        static final TimeZoneNumberRule INSTANCE_COLON    = new TimeZoneNumberRule(true);

        static final TimeZoneNumberRule INSTANCE_NO_COLON = new TimeZoneNumberRule(false);

        final boolean                   mColon;

        /**
         * Constructs an instance of {@code TimeZoneNumberRule} with the specified properties.
         *
         * @param colon
         *            add colon between HH and MM in the output if {@code true}
         */
        TimeZoneNumberRule(final boolean colon){
            mColon = colon;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return 5;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{

            int offset = calendar.get(Calendar.ZONE_OFFSET) + calendar.get(Calendar.DST_OFFSET);

            if (offset < 0){
                buffer.append('-');
                offset = -offset;
            }else{
                buffer.append('+');
            }

            final int hours = offset / (60 * 60 * 1000);
            appendDigits(buffer, hours);

            if (mColon){
                buffer.append(':');
            }

            final int minutes = offset / (60 * 1000) - 60 * hours;
            appendDigits(buffer, minutes);
        }
    }

    /**
     * <p>
     * Inner class to output a time zone as a number {@code +/-HHMM}
     * or {@code +/-HH:MM}.
     * </p>
     */
    private static class Iso8601_Rule implements Rule{

        // Sign TwoDigitHours or Z
        static final Iso8601_Rule ISO8601_HOURS               = new Iso8601_Rule(3);

        // Sign TwoDigitHours Minutes or Z
        static final Iso8601_Rule ISO8601_HOURS_MINUTES       = new Iso8601_Rule(5);

        // Sign TwoDigitHours : Minutes or Z
        static final Iso8601_Rule ISO8601_HOURS_COLON_MINUTES = new Iso8601_Rule(6);

        /**
         * Factory method for Iso8601_Rules.
         *
         * @param tokenLen
         *            a token indicating the length of the TimeZone String to be formatted.
         * @return a Iso8601_Rule that can format TimeZone String of length {@code tokenLen}. If no such
         *         rule exists, an IllegalArgumentException will be thrown.
         */
        static Iso8601_Rule getRule(final int tokenLen){
            switch (tokenLen) {
                case 1:
                    return ISO8601_HOURS;
                case 2:
                    return ISO8601_HOURS_MINUTES;
                case 3:
                    return ISO8601_HOURS_COLON_MINUTES;
                default:
                    throw new IllegalArgumentException("invalid number of X");
            }
        }

        final int length;

        /**
         * Constructs an instance of {@code Iso8601_Rule} with the specified properties.
         *
         * @param length
         *            The number of characters in output (unless Z is output)
         */
        Iso8601_Rule(final int length){
            this.length = length;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int estimateLength(){
            return length;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public void appendTo(final Appendable buffer,final Calendar calendar) throws IOException{
            int offset = calendar.get(Calendar.ZONE_OFFSET) + calendar.get(Calendar.DST_OFFSET);
            if (offset == 0){
                buffer.append("Z");
                return;
            }

            if (offset < 0){
                buffer.append('-');
                offset = -offset;
            }else{
                buffer.append('+');
            }

            final int hours = offset / (60 * 60 * 1000);
            appendDigits(buffer, hours);

            if (length < 5){
                return;
            }

            if (length == 6){
                buffer.append(':');
            }

            final int minutes = offset / (60 * 1000) - 60 * hours;
            appendDigits(buffer, minutes);
        }
    }

    // ----------------------------------------------------------------------
    /**
     * <p>
     * Inner class that acts as a compound key for time zone names.
     * </p>
     */
    private static class TimeZoneDisplayKey{

        private final TimeZone mTimeZone;

        private final int      mStyle;

        private final Locale   mLocale;

        /**
         * Constructs an instance of {@code TimeZoneDisplayKey} with the specified properties.
         *
         * @param timeZone
         *            the time zone
         * @param daylight
         *            adjust the style for daylight saving time if {@code true}
         * @param style
         *            the timezone style
         * @param locale
         *            the timezone locale
         */
        TimeZoneDisplayKey(final TimeZone timeZone, final boolean daylight, final int style, final Locale locale){
            mTimeZone = timeZone;
            if (daylight){
                mStyle = style | 0x80000000;
            }else{
                mStyle = style;
            }
            mLocale = locale;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int hashCode(){
            return (mStyle * 31 + mLocale.hashCode()) * 31 + mTimeZone.hashCode();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean equals(final Object obj){
            if (this == obj){
                return true;
            }
            if (obj instanceof TimeZoneDisplayKey){
                final TimeZoneDisplayKey other = (TimeZoneDisplayKey) obj;
                return mTimeZone.equals(other.mTimeZone) && mStyle == other.mStyle && mLocale.equals(other.mLocale);
            }
            return false;
        }
    }
}
